The fracture behavior of birch and spruce in the radial-tangential crack propagation direction at the scale of the growth ring

Holzforschung ◽  
2013 ◽  
Vol 67 (6) ◽  
pp. 673-681 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Mouth Opening ◽  
Crack Tip ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Crack Model ◽  
Pure Mode ◽  
Displacement Fields ◽  
Tip Displacement

Abstract Crack-tip displacement fields have been computed based on digital image correlation for spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood, which were submitted to pure mode I loading in the RT-direction under both green and air-dried conditions. Moreover, crack propagation was modeled based on both linear elastic fracture mechanics (LEFM) and nonlinear fracture mechanics, relying on the fictitious crack model (FCM). The measured and modeled load versus the crack-mouth opening displacement (CMOD) curves and displacement fields were compared. In the case of spruce, the load-CMOD curves simulated by the FCM coincide well with the measured ones. On the contrary, measured near crack-tip displacement fields in both green and air-dried spruce are better comparable with the LEFM predictions than with the FCM predictions. In the case of green birch, the simulated FCM curve follows the measured curve quite well, but in air-dried birch the simulated FCM curve has a better fit than the LEFM-curve only before maximum load. In birch, the FCM predicts the displacement fields better than the LEFM. In both species, moisture content has a big effect on the softening behavior. In both spruce and birch, the FCM overestimates the displacements ahead of crack tip, whereas the LEFM model underestimates the displacements.

The cellular level mode I fracture behaviour of spruce and birch in the RT crack propagation system

Holzforschung ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Crack Propagation ◽  
Fracture Behaviour ◽  
Crack Tip ◽  
Cellular Level ◽  
Image Correlation ◽  
Environmental Scanning ◽  
Mode I ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Displacement Fields

Abstract The effect of the microscopic structure and the moisture content (MC) of wood on its fracture behaviour has been investigated. Green and air-dried spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood were subjected to pure mode I loading in the radial- tangential (RT) crack propagation system. Tests were carried out in situ in an environmental scanning electron microscope to observe crack propagation at the cellular level. Crack-tip displacement fields were computed by digital image correlation, and crack propagation was observed from the images captured during testing. Both the MC and the microscopic structure were found to affect the fracture process. In the air-dried birch and spruce, only microcracking caused large displacements ahead of the crack-tip. In spruce, the microcracking zone was larger than in birch. In green birch and spruce, microcracking was less evident than in the air-dried specimens, and in some cases, there were notable deformations in a few cells ahead of the crack-tip before crack extension. Microcracking is considered to be the main toughening mechanism in spruce and birch in the RT crack propagation system.

The effect of temperature and moisture content on the fracture behaviour of spruce and birch

Holzforschung ◽  
2016 ◽  
Vol 70 (4) ◽  
pp. 369-376 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Moisture Content ◽  
Crack Propagation ◽  
Fracture Behaviour ◽  
Mouth Opening ◽  
Climatic Conditions ◽  
Effect Of Temperature ◽  
Crack Mouth Opening Displacement ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Opening Displacement

Abstract The fracture behaviour of wood is affected by, amongst other factors, its microscopic structure, moisture content and temperature, as well as the direction of crack propagation. Spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) compact tension specimens were subjected to pure mode I loading in both the radial-tangential (RT) and tangential-radial (TR) orientations under four climatic conditions. The effect of microscopic structure on crack propagation was observed, and the “crack mouth opening displacement vs. load” histories were recorded, from which characteristic fracture parameters were calculated. The fracture surfaces were subsequently examined by optical microscopy. In both species, distinct changes in the fracture behaviour were observed as moisture content (MC) and temperature (T) were varied. The results were specific for the wood species, but MC and T influenced fracture behaviour in a similar way. The effects were more pronounced in birch than in spruce. Elevated T and MC did not affect the failure mode, except in the case of spruce in the RT orientation.

Comparison study of crack propagation in rubberized and conventional prestressed concrete sleepers using digital image correlation

2021 ◽  
pp. 095440972110205
Author(s):  
Guoqing Jing ◽  
Du yunchang ◽  
Ruilin You ◽  
Mohammad Siahkouhi
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Prestressed Concrete ◽  
Mouth Opening ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Experimental Program ◽  
Pure Bending ◽  
Opening Displacement ◽  
Rubber Concrete

Rubber concrete (RC) has been confirmed to be suitable for concrete sleeper production. This paper studies the cracking behaviour of conventional and rubber-reinforced concrete sleepers based on the results of an experimental program. The cracking behaviour in the pure bending zone was analysed up to a load of 140 kN. The crack mouth opening displacement (CMOD) was accordingly measured using a digital image correlation (DIC) method. The DIC results show that the rubber prestressed concrete sleeper (RPCS) has a resistance against crack initiation that is 20% greater than that of the conventional prestressed concrete sleeper (CPCS) under the same loading condition; however, due to the higher crack growth rate of the RPCS, the first crack detected by the operator forms at 60 kN, which corresponds to a strength approximately 9% lower compared with the 65 kN load at which the first crack is detected in the CPCS. Before the first crack (60 kN), the RPCS has a deflection 35% lower than that of the CPCS, but after cracking, at loads of 80 kN, 100 kN and 140 kN, the RPCS has a deflection 15%, 4% and 24% higher than that of the CPCS, respectively.

The Bridged Crack Model for the Analysis of Brittle Matrix Fibrous Composites Under Repeated Bending Loading

2007 ◽  
Vol 74 (6) ◽  
pp. 1239-1246 ◽  
Author(s):  
Alberto Carpinteri ◽  
Simone Puzzi
Keyword(s):  
Reinforced Concrete ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Composite Beam ◽  
Crack Model ◽  
Brittle Matrix ◽  
Cyclic Bending ◽  
Mechanics Model ◽  
Bending Loading ◽  
Bridged Crack

In this paper, we present a fracture-mechanics based model, the so-called bridged crack model (Carpinteri, A., 1981, “A Fracture Mechanics Model for Reinforced Concrete Collapse,” Proc. of IABSE Colloquium on Advanced Mechanics of Reinforced Concrete, Delft, I.A.B.S.E., Zürich, pp. 17–30; Carpinteri, A., 1984, “Stability of Fracturing Process in R.C. Beams,” J. Struct. Engng. (A.S.C.E.), 110, pp. 544–558) for the analysis of brittle matrix composites with discontinuous ductile reinforcements under the condition of repeated bending loading. In particular, we address the case of composites with very high number of reinforcements (i.e., fiber-reinforced composites, rather than conventionally reinforced concrete). With this aim, we propose a new iterative procedure and compare it to the algorithm recently proposed by Carpinteri, Spagnoli, and Vantadori (2004, “A Fracture Mechanics Model for a Composite Beam with Multiple Reinforcements Under Cyclic Bending,” Int. J. Solids Struct., 41, pp. 5499–5515), showing the advantages in terms of computational efficiency. Furthermore, we analyze the combined effects of crack length, brittleness number, and fiber number on the cyclic behavior of the composite beam, showing the conditions enhancing the energy dissipation in the composite system. Eventually, we analyze crack propagation and propose, consistently with the model premises, a fracture-mechanics-based crack propagation criterion that allows one to simulate cyclic bending tests under the fixed grip condition.

Crack propagation in a PVA dual-crosslink hydrogel: Crack tip fields measured using digital image correlation

2019 ◽  
Vol 138 ◽  
pp. 103158 ◽  
Author(s):  
Mincong Liu ◽  
Jingyi Guo ◽  
Zhilong Li ◽  
Chung-Yuen Hui ◽  
Alan T. Zehnder
Keyword(s):  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Crack Tip ◽  
Image Correlation ◽  
Crack Tip Fields

scholarly journals Identification and Prediction of Mixed-Mode Fatigue Crack Path in High Strength Low Alloy Steel

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 504
Author(s):  
Jie Zhang ◽  
Cedric Kiekens ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Mixed Mode ◽  
Standardized Test ◽  
Crack Tip ◽  
Shear Loading ◽  
Image Correlation ◽  
Crack Trajectory

The trajectory of fatigue crack growth is influenced by many parameters and can be irregular due to changes in stress distribution or in material properties as the crack progresses. Images of the surface of a standardized test specimen can be used to visualize the crack trajectory in a non-destructive way. Accurately identifying the location of the crack tip, however, is challenging and requires devoted image postprocessing. In this respect, digital image correlation allows to obtain full field displacement and strain fields by analysing changes of digital images of the same sample at different stages of loading. This information can be used for the purpose of crack tip tracking. This paper presents a combined experimental-numerical study of detection and prediction of fatigue crack propagation path by means of digital image correlation (DIC) and the extended finite element method (X-FEM). Experimental validation and analyses are carried out on a modified C(T) specimen in which a curved crack trajectory is triggered by introducing mixed-mode (tension + shear) loading. The developed tools are used for validating an automated framework for crack propagation prediction.

Test for Crack Opening Displacement of Steel Fiber Reinforced Concrete under Three-Point Bending

2010 ◽  
Vol 36 ◽  
pp. 157-161 ◽  
Author(s):  
Tin Gyi Zhang ◽  
Yuan Bao Leng ◽  
Dan Ying Gao
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Mouth Opening ◽  
Crack Tip ◽  
Crack Mouth Opening Displacement ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Critical Crack Opening ◽  
Crack Tip Opening

Based on the principle of electrical measurement method, the clip gauge was made to measure the crack opening displacement (COD).Through the three-point bending test on the specimens of steel fiber reinforced high strength concrete (SFHSC), the effect of the fiber volume fraction (ρf) upon the critical crack opening displacement (the critical crack tip opening displacement and the critical crack mouth opening displacement) was studied. The result shows that the effect of ρf on mouth-tip ratio (the ratio of critical crack mouth opening displacement to critical crack tip opening displacement) can reflect its effect upon the critical crack opening displacement. According to the geometrical relationship between the initial crack length and the critical crack opening displacement，calculation method for the initial crack length was proposed. Based on the test result, the formula was established for calculating the critical crack tip opening displacement.

scholarly journals Vibrated Concrete vs. Self-Compacting Concrete: Comparison of Fracture Mechanics Properties

2014 ◽  
Vol 601 ◽  
pp. 199-202
Author(s):  
Sara Korte ◽  
Veerle Boel ◽  
Wouter de Corte ◽  
Geert de Schutter
Keyword(s):  
Fracture Mechanics ◽  
Mouth Opening ◽  
Bending Test ◽  
Crack Mouth Opening Displacement ◽  
Self Compacting Concrete ◽  
Opening Displacement ◽  
Three Point Bending ◽  
Fracture Parameters ◽  
Wedge Splitting Test ◽  
Splitting Test

This study focuses on the fracture mechanics aspect of self-compacting concrete, compared to vibrated concrete. The most commonly used experiments to investigate the toughness and cracking behaviour of concrete are the three-point bending test (3PBT) on small, notched beams, and the wedge-splitting test (WST) on cubic samples with guiding groove and starter notch. From the resulting P-CMOD curves (applied load versus crack mouth opening displacement), different fracture parameters, such as fracture energy and fracture toughness, can be extracted. Moreover, using inverse analysis, the σ-w relationship (tensile stress versus crack width) can be derived. This paper lists the results of a series of tests on samples, made of VC, SCC of equal strength, and SCC with identical w/c factor. Subsequently, a comparison of the mechanical characteristics is made, revealing important differences regarding several fracture parameters.

An Improved CEM with Regard to the Crack-Tip

2014 ◽  
Vol 989-994 ◽  
pp. 908-912
Author(s):  
Yong Sheng Lin
Keyword(s):  
Stress Intensity ◽  
Crack Tip ◽  
Partition Of Unity ◽  
Displacement Fields ◽  
Basic Principles ◽  
Displacement Mode ◽  
Composite Element Method ◽  
Local Enrichment ◽  
Similar Accuracy ◽  
Tip Displacement

This paper expounds the basic principles of composite element method (CEM).In order to model the discontinuity of the displacement, the asymptotic crack tip displacement fields are added to the CEM approximation for the local enrichment by using the framework of partition of unity. Thus, the crack tip can be inserted into anywhere within the element. The crack-tip displacement mode is given, and some formulas are derived and established in a CEM program. The evaluation of stress intensity is discussed. Numerical simulations illustrate that the proposed algorithm has similar accuracy compared to the FEM, and it has advantage of convenient of pre-process.

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